Process for decontaminating radioactive objects

ABSTRACT

A process for decontaminating radioactive objects by washing them in a solution of Alpha -amino (alkane-phosphonic) acid and a tensio-active substance that has been neutralized to a pH from 7 to 7.5 and diluted to a 10 percent concentration. The wash effluents are decontaminated by adding to the effluents sufficient calcium-ions to displace the rare earths and strontium from their complexes with Alpha -amino (alkane-phosphonic) acid and thereafter scrubbing.

States Patent msmm Werot et al. [451 Apr. M, 1972 [54] PROCESS FOR DECONTAMINATING References Cited RADIOAUHVE UBJECTS UNITED STATES PATENTS [72] Inventors: Jean-Louis Verot, Saint-Cyr LEcole; Rene 2,924,576 2/ 1960 Bersworth et al. 1 34/29 UX Sarfati, Paris, both of France 3,234,124 2/1966 lrani 1 34/42 X [73] Assignee: Ugine Kuhlmann, Paris, France Primary Examiner Morris w 01k [22] Filed: Aug. 14, 1968 Assistant Examiner-Joseph T. Zatarga Anorney-Webb, Burden, Robinson & Webb [21] Appl. No.: 752,504

[57] ABSTRACT Foreign Application Priority A process for decontaminating radioactive objects by washing n 1 them in a solution of a-amino (alkane-phosphonic) acid and a Aug 1967 France 1 8019 tensio-active substance that has been neutralized. to a pH from 7 to 7.5 and diluted to a 10 percent concentration. The wash lll ..134/26, 84/432682 effluents are decontaminated y adding to the effluents sum {58] Fie'ld 210/58 cient calcium-ions to displace the rare earths and strontium from their complexes with a-amino (alkane-phosphonic) acid 7 and thereafter scrubbing.

11 Claims, No Drawings PROCESS lFOlR DECONTAMINATING RADIOACTIVE OBJECTS Linen and other materials used in nuclear equipment and processes involving radioactivity must be thoroughly cleaned and decontaminated before they can be reused. It is also necessary that the wash effluents be purified of radioactivity by scrubbing. However, the usual methods of cleansing has not proven efficient.

To increase the cleansing efficiency, the use of very strong chelates, for example, derivatives of ethylene-diaminetetracetic acid has been proposed. Under the influence of these chelates, the radioactive elements lose their chemical individuality and the washing effluents containing these elements cannot be subjected to a coprecipitation treatment. Furthermore, the evaporation treatment of the wash effluents is not practical because the presence of tensio-active agents considerably reduces the output of the evap'orators.

We have invented a process for the efficient decontamination of radioactive objects, the wash effluents of which are easily scrubbed. Generally, our process utilizes the complexing properties of a-amino (alkane-phosphonic) acids, and, in particular, those amino-tri (methane-phosphonic) acids produced by Monsanto Chemical Company under thetrademark Dequest." These acids form complexes with ions having a valence equal to or greater than 2. These complexes are stable in solutions which are slightly acidic, neutral, or alkaline; yet, the complexes are sufficiently labile so that the radioactive elements may be displaced from them, for example, by an excess of precipitating agent.

According to our process, various objects may be decontaminated by washing them with a solution at a temperature between 60 and 90 C, of a mixture of a tensio-active substance and a nearly neutral sodium salt of an a-amino (alkanephosphonic) acid in water, preferably deionized water. The tensio-active substance is preferably an entirely biodegradable, for example, a heavy alcohol having a straight oxyethylated chain. The wash effluents are scrubbed by coprecipitation or by treatment of zeolites after calcium-ions have been added to the effluents.

The tensio-active substances are preferably biodegradable products such as oxyethylation products of the heavy straight chain alcohols, for example, Plurafacs. Alcohol sulfates and sulfonates also give good results. However, tensio-active substances that are not biodegradable, or only partially so, may be used. We have found that alkylaryl sulfates or sulfonates, oxyethylated derivatives of polypropylene glycol, such as Emkalyx-Pluraonics, oxyethylated alkyl-phenols and oxyethylated or oxypropylated derivatives of ethylene-diamine such as Tetronics give efficient results.

Generally, in carrying out our process, a solution, in deionized water, of from to 500 g/liter of a-amino (alkanephosphonic) acid solution and from to 500 g/liter of tensioactive substance is prepared. This solution is neutralized, preferably with sodium hydroxide, to obtain a pH from 7 to 7.5. This neutralized solution is the mother-solution. The washing solution results from the dilution of approximately 10 percent of the mother-solution in water, preferably deionized water. If desired, adjuvants such as disinfectants, optical brighteners, etc. may be added. The concentration of the washing solution is set in accordance with the strain degree of the objects decontaminated. The soaking of the objects to be decontaminated in the washing solution, in some cases, must be accompanied with a strong brushing.

With the use of this process, we have obtained a very high degree of decontamination. After treatment, the decontaminated object has been found to have a radioactive count indistinguishable from the background count.

The effluents resulting from the wash generally have a slight or medium activity (10 l0 Ci/m). Calcium in the form of calcium nitrate or calcium chloride is added to the wash effluent in an amount to give an ionic-concentration sufiicient to displace the rare earths and strontium from their complexes with the a-amino (alkane-phosphonic) acid. For example, the

calcium-ion quantity is generally less than 1/100 of equivalent-gram per liter of solution.

After the calcium has been added to the wash effluents, the effluents are scrubbed in the usual manner. For instance, they may be scrubbed by coprecipitation or, preferably, by means of zeolites. The treatment with zeolites has an excellent scrubbing output.

The following examples relate to the decontamination of objects used in nuclear instruments or equipment and to the treatment of the resulting effluent.

EXAMPLE I Decontamination of Linen A solution in deionized water was prepared having 50 g/liter of a solution of Plurafac RA No. 20 alcohol and 50 g/liter of a solution of amino-tri(methane-phosphonic) acid. The solution was neutralized by the addition of sodium hydroxide to form the mother-solution. The mother-solution was diluted in deionized water to form a 10 percent solution. The linen was then washed in the 10 percent wash solution at a temperature between and C. At the end of the washing, the normal checking instruments indicated no radioactivity on the linen.

EXAMPLE II Decontamination of Laboratory Material Laboratory material comprising iron, steel, stainless steel, duralumin, aluminum, copper, brass, polystyrene, nylon, polyethylene, polyvinyl chloride, porcelain, and glass pieces was decontaminated. With regard to glass, care should be taken to dip it immediately after use for efiicient decontamination.

A solution in the deionized water contained 40 g/liter of solution of Plurafac RA No. 40 alcohol and 70 g/liter of amino-tri (methane-phosphonic) acid. The solution was neutralized to a pH of 7 to 7.5 with sodium hydroxide to give a mother-solution. The mother-solution was diluted in deionized water to obtain a solution of 10 percent concentration. The 10 percent solution was brought to a temperature of 60 and the various objects were soaked with an accompanying damp brushing.

After the foregoing treatment, the radiation count of the various objects was indistinguishable from the background count.

EXAMPLE Ill Decontamination of the Wash Effluent The wash effluent from the treatment of Example ll had an apparent activity of 11,600 impulses/m1 for 5 minutes. To the wash effluent was added 0.5 g/liter of calcium-ions in the form of calcium nitrate. The solution was then divided into three parts, each of which was separately scrubbed:

a. the first part, after treatment by precipitation of calcium carbonate, had an apparent activity of 965 impulses/ml for 5 minutes. The decontamination factor was 1 2.

b. the second part, after treatment by precipitation of calcium phosphate had an apparent activity of 580 impulses/ml for 5 minutes. The decontamination factor was 20.

c. the third part, after treatment by scattering of zeolite and filtration, had an apparent activity of 128 impulses/ml for 5 minutes. The decontamination factor was 90.

While we have described certain embodiments of our invention, it is to be understood that it may be otherwise embodied within the scope of the appended claims.

We claim:

1. A process for decontamination of radioactive objects comprising:

A. preparing a solution of a-amino (alkanephosphonic) acid and tensio-active substance, in water;

B. substantially neutralizing said solution;

C. washing a radioactive object with said substantially neutralized solution; and,

D. treating said solution, after it is used for washing, with calcium ions and scrubbing said solution.

2. A process for the decontamination of radioactive objects having radioactive rare earths or strontium particles thereon comprising:

A. preparing a solution of from to 500 g/liter of a-amino (alkane-phosphonic) acid and from 10 to 500 g/liter of a tensio-active substance in deionized water;

B. neutralizing said solution to a pH of from about 7 to about 7.5 with sodium hydroxide;

C. washing said radioactive object with said solution, such that said particles are complexed with said a-amino (alkane-phosphonic)acid; and,

D. treating said solution with calcium ions sufficient to displace said particles from their complexes and scrubbing said solution.

3. The process of claim 2 wherein said tensio-active substance is biodegradable.

4. The process of claim 2 wherein said tensio-active substance is a heavy alcohol with a straight oxyethylated chain.

5. The process of claim 2 wherein said solution after neutralization is diluted in deionized water to a concentration of 10 percent.

6. The process of claim 2 wherein said solution has added thereto at least one of disinfectants and optical brighteners.

7. The process of claim 2 wherein the solution is scrubbed by coprecipitation.

8. The process of claim 2 wherein the solution is scrubbed by scattering with zeolite and filtering.

9. The process of claim 2 wherein said acid is amino-tri (methane-phosphonic) acid.

10. The process of claim 9 wherein the calcium ions are supplied by adding calcium nitrate to the solution after washing.

11. The process of claim 10 wherein the solution is scrubbed by coprecipitation of a salt selected from the group calcium phosphate and calcium sulphate. 

2. A process for the decontamination of radioactive objects having radioactive rare earths or strontium particles thereon comprising: A. preparing a solution of from 10 to 500 g/liter of Alpha -amino (alkane-phosphonic) acid and from 10 to 500 g/liter of a tensio-active substance in deionized water; B. neutralizing said solution to a pH of from about 7 to about 7.5 with sodium hydroxide; C. washing said radioactive object with said solution, such that said particles are complexed with said Alpha -amino (alkane-phosphonic)acid; and, D. treating said solution with calcium ions sufficient to displace said particles from their complexes and scrubbing said solution.
 3. The process of claim 2 wherein said tensio-active substance is biodegradable.
 4. The process of claim 2 wherein said tensio-active substance is a heavy alcohol with a straight oxyethylated chain.
 5. The process of claim 2 wherein said solution after neutralization is diluted in deionized water to a concentration of 10 percent.
 6. The process of claim 2 wherein said solution has added thereto at least one of disinfectants and optical brighteners.
 7. The process of claim 2 wherein the solution is scrubbed by coprecipitation.
 8. The process of claim 2 wherein the solution is scrubbed by scattering with zeolite and filtering.
 9. The process of claim 2 wherein said acid is amino-tri (methane-phosphonic) acid.
 10. The process of claim 9 wherein the calcium ions are supplied by adding calcium nitrate to the solution after washing.
 11. The process of claim 10 wherein the solution is scrubbed by coprecipitation of a salt selected from the group calcium phosphate and calcium sulphate. 